Power converters may generally include switches and one or more capacitors. Such converters can be used, for example, to power portable electronic devices and consumer electronics.
A switch-mode power converter is a specific type of power converter that regulates an output voltage or current by switching energy storage elements (i.e. inductors and capacitors) into different electrical configurations using a switch network.
A switched capacitor converter is a type of switch-mode power converter that primarily utilizes capacitors to transfer energy. In such converters, the number of capacitors and switches increases as the transformation ratio increases.
Typical power converters perform voltage transformation and output regulation. In many power converters, such as buck converters, both functions take place in a single stage. However, it is also possible to split these two functions into two specialized stages. Such two-stage power converter architectures feature a separate transformation stage and a separate regulation stage. The transformation stage transforms one voltage into another voltage, while the regulation stage ensures that the output voltage and/or output current of the power converter maintains desired characteristics.
For example, referring to FIG. 1, in one known power converter 10, a switched capacitor element 12A is electrically connected, at an input end thereof, to a voltage source 14. An input of a regulating circuit 16A is electrically connected to an output of the switched capacitor element 12A. A load 18A is then electrically connected to an output of the regulating circuit 16A. Such a converter is described in US Patent Publication 2009/0278520, filed on May 8, 2009, the contents of which are herein incorporated by reference.
Furthermore, a modular multi-stage power converter architecture is described in PCT Application PCT/2012/36455, filed on May 4, 2012, the contents of which are also incorporated herein by reference. The switched capacitor element 12A and the regulating circuit 16A can be mixed and matched in a variety of different ways. This provides a transformative integrated power solution (TIPS™) for the assembly of such power converters. As such, the configuration shown in FIG. 1 represents only one of multiple ways to configure one or more switched capacitor elements 12A with one or more regulating circuits 16A.
FIG. 2 illustrates a power converter 10A that receives an input voltage VIN from the voltage source 14 and produces an output voltage VO that is lower than the input voltage VIN. The power converter 10A is a particular embodiment of the power converter architecture illustrated in FIG. 1. The switched capacitor element 12A features a 2:1 dual-phase series-parallel switched capacitor network that includes power switches S1-S8 and pump capacitors C1-C2. In contrast, the regulating circuit 16A features a buck converter that includes a low-side switch SL, a high-side switch SH, a filter inductor L1, and a driver stage 51.
In the operation of the switched capacitor element 12A, the power switches S1, S3, S6, S8 and the power switches S2, S4, S5, S7 are always in complementary states. Thus, in a first network state, the power switches S1, S3, S6, S8 are open and the power switches S2, S4, S5, S7 are closed. In a second network state, the power switches S1, S3, S6, S8 are closed and the power switches S2, S4, S5, S7 are open. The switched capacitor element 12A cycles through the first network state and the second network state, resulting in an intermediate voltage VX that is one-half of the input voltage VIN.
Referring to FIG. 2, the switched capacitor element 12A is in the first network state when a first phase voltage VA is low and a second phase voltage VB is high. In contrast, the switched capacitor element 12A is in the second network state when the first phase voltage VA is high and the second phase voltage VB is low. The two phase voltages VA, VB are non-overlapping and have approximately a fifty percent duty cycle.
In the operation of the regulating circuit 16A, the low-side switch SL and the high-side switch SH chop the intermediate voltage VX into a switching voltage VLX. A LC filter receives the switching voltage VLX and generates the output voltage VO that is equal to the average of the switching voltage VLX. To ensure the desired output voltage VO, a regulation control voltage VR controls the duty cycle of the low-side switch SL and the high-side switch SH. Additionally, the driver stage 51 provides the energy to open and close the low-side and high-side switches SL, SH.
Previous disclosures treat the control of the switched capacitor element 12A and regulating circuit 16A separately. This has numerous disadvantages, one of which is that the intermediate voltage VX ripple will feed through to the output voltage VO. A possible solution to this problem is to create a feed-back control loop that is fast enough to attenuate the effect of the intermediate voltage VX ripple on the output voltage VO. To achieve this goal, the frequency of the regulating circuit 16A must be at a significantly higher frequency than the frequency of the switched capacitor element 12A.
Another possible solution to this problem would be to add a feed-forward control loop to the regulating circuit 16A. However, as was the case with the fast feed-back solution, the feed-forward solution will only be effective if the frequency of the regulating circuit 16A is significantly higher than the frequency of the switched capacitor element 12A. Therefore, both solutions place a severe frequency constraint on the switched capacitor element 12A and the regulating circuit 16A.
Furthermore, there is typically a dead-time interval DT between the first network state and the second network state of the switched capacitor element 12A. During the dead-time interval DT, all of the switches in the switched capacitor element 12A are open. This ensures a clean transition between the first network state and the second network state of the switched capacitor element 12A, and vice versa. If the regulating circuit 16A tries to draw current during the dead-time interval DT, a voltage ‘glitch’ will occur at the node between the switched capacitor element 12A and the regulating circuit 16A.
The voltage ‘glitch’ can be reduced through the use of a glitch capacitor CX. Unfortunately, a portion of the energy stored on the glitch capacitor CX is thrown away each time the switched capacitor element 12A transitions between the first network state and the second network state, and vice versa. The energy loss is a result of the glitch capacitor CX being shorted to capacitors at a different voltage, such as pump capacitors C1, C2. Therefore, the use of a glitch capacitor CX to supply energy during the dead-time interval DT is an effective solution, but requires one additional capacitor and reduces the efficiency of the power converter 10A.